Hmm, there are many points in your post that I strongly disagree with.
Name Brands; Epic Armoury, Calimacil, Artilier Nemesis, Forgotten Dreams are the main manufacturer of latex and foam injection swords.
You didn't mention there is a different between latex and foam injection swords. Latex coated swords, which are usually made from open cell foam, require some maintenance. That maintenance is silicone spray on the latex. The silicone helps keep the latex moist and slow down its aging. Foam injection sword blades do not require this.
The first two photos show foam injection blades, and the first one is Calimacil. The foam injection blades are know to have a firmer blade than the latex coated blades. Epic Armoury is the best known manufacturer of latex coated blades. One thing about latex is that some LARPs may require a cover over the blade due to some players having a latex allergy (I have seen this happen).
As for heat, I know the latex blades can withstand sitting in very hot cars, and for foam injection blades, they have even a higher heat tolerance.
The cost of a LARP-safe sword is more than $50, and a boffer would be more than $5, unless you have most of the materials yourself and only need to buy duct-tape.